Behavior maintained and controlled by scheduled injections of drugs in nonhuman primates serves as an experimental model of drug-seeking behavior in man. The objective of this research isto analyze behavioral and pharmacological features that determine how a drug will alter behavior that precedes its injection. Experiments on behavior controlled by scheduled injections of psychomotor stimulants (e.g., cocaine or amphetamine), barbiturates, or narcotic analgesics (e.g., morphine) will be conducted in the squirrel monkey and the rhesus monkey. Characteristics of performance under fixed-interval, fixed-ratio, second-order, and various other schedules of drug injection will be studied to establish similarities and differences among drugs that can function as reinforcers. Some experiments will be concerned with the effects of physiological dependence on responding under fixed-interval schedules of morphine or methohexital injection. Schedule-controlled patterns of responding will be used to make comparisons among various drugs that function as reinforcers and between drug injection and other events (e.g., food or electric shock) that function as reinforcers. The conditions under which injections of certain drugs (e.g., naloxone or chlorpromazine) can be used to suppress responding (punishment) will be investigated. The effects on schedule-controlled behavior of pretreatments with drugs of various classes, especially drugs that can function as reinforcers or punishers, will be studied. The overall objective of this research will be to specify behavioral and pharmacological variables, past and present, that determine how drugs control behavior.